Use underscored variables automatically for dasherized params

[kurko]

Here's what we have to do to support parameters with dashed (e.g JSONAPI):

parameter 'application-id', "Application ID"

let(:application_id)  { application.id }
let('application-id') { application_id }

Dashed parameters should just use the underscored version of the name. application-id would look up for application_id.